The present invention relates to a system for drying web material and more particularly, to a system utilizing nozzles which can be removed and/or adjusted conveniently and quickly.
For nearly two centuries, the dominant system for drying continuous webs has been a series of rotating steam heated cylinders. When drying surface coatings on paper webs, the alternating contact of the web with the metal cylinder results in picking and other quality defects. This problem was a primary stimulus for the development of flotation drying systems that simultaneously support and convectively dry the web on a cushion of high velocity hot air. In the past twenty years, flotation drying has evolved into the dominant method for drying coated webs. Examples of nozzle assemblies utilized for flotation drying are taught by U.S. Pat. Nos. 3,587,177 and 4,414,757.
With a typical flotation web drying installation, the drying is accomplished by an array of nozzles positioned on each side of the web. Heated air is transported to the nozzles by a system of headers to which the air is supplied by ducts. A similar duct collects the air after it leaves the vicinity of the web.
There are various types of flotation drying nozzles. One known type of nozzle, which is taught by U.S. Pat. Nos. 3,587,177, the teachings of which are incorporated herein by reference, utilizes a "negative" pressure gas cushion to support and dry the web. U.S. Pat. No. 4,414,757 teaches another known type of nozzle, utilizing a "positive" pressure to float and dry the web, and the teachings of this patent are also incorporated herein by reference. This nozzle also imparts an undulating web flow characteristic which is preferable for most drying applications, and such nozzles display very uniform machine-direction heat transfer. Positive pressure nozzles are tolerant of a very large range of web tensions, and they allow the web to resist the formation of edge curls.
Flotation drying systems utilizing either type of nozzles, however, have not proven to be easily adaptable for use in special applications. In laboratory research and development work, it is highly desirable to have a method of quickly changing nozzle spacings to develop heat transfer data. In production applications, it is desirable to have a method of quick removal for cleaning and quick replacement to an exact previous location to maintain exact heat transfer characteristics. In known nozzle assemblies, these objectives cannot be obtained.
Accordingly, it is an object of the present invention to provide a nozzle assembly for use in flotation drying systems which can be quickly assembled and disassembled.
It is another object of the present invention to provide a nozzle assembly for flotation drying systems which incorporates a method of quickly changing nozzle spacings to develop heat transfer data.
It is a further object of the present invention to provide a nozzle assembly for flotation drying systems, which can be quickly removed for cleaning and/or quickly replaced to the exact previous location to maintain exact heat transfer characteristics of the web.